System and Method for Performing Nano Beam Diffraction Analysis

ABSTRACT

A system for performing diffraction analysis, includes a mill for removing a surface portion of a sample, and an analyzer for performing diffraction analysis on the milled sample.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application is a Continuation Application of U.S. patentapplication Ser. No. 15/908,400, filed on Feb. 28, 2018, which is aContinuation Application of U.S. patent application Ser. No. 15/199,350,filed on Jun. 30, 2016 (Now U.S. Pat. No. 9,978,560), and incorporatedherein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a system and method for performing nanobeam diffraction (NBD) analysis and, more particularly to a system andmethod of performing NBD analysis which includes additional thinning ofa focused ion beam (FIB) prepared transmission electron microscopy (TEM)sample. The additional milling is done to remove a damaged portion ofthe TEM sample.

Description of the Related Art

Convergent beam electron diffraction (CBED), nano beam electrondiffraction (NBD), dark field holography, and experimental/modelingelectron diffraction contrast imaging (EDCI) techniques are all validways to measure strain in single crystalline materials such as thosefound in semiconductor devices.

Of these, NBD has become one of the preferred methods for performingthis type of analysis due to its relative ease of use and relativelystraight forward interpretation. At NBD's fundamental level it looks atrelative changes in atomic planes in a single crystalline material bylooking at the displacement of diffraction spots in diffraction patternscompared to a reference pattern.

The spacing between the diffraction spots in a diffraction patterndirectly correlate to the spacing between crystallographic planes in thecrystalline material generating the pattern. The reference diffractionpattern is typically obtained from an unstrained region within thesample. It is then straightforward to calculate the strain (or latticemismatch if multiple single crystalline materials are involved) of allthe other diffraction patterns with respect to the reference wherestrain (ε) is:

ε=ΔL/L ₀=(L ₁ −L ₀)/L ₀

where L₀ is the distance between the diffraction spot of interest andthe directly transmitted spot in the reference diffraction pattern, L₁is the distance between the diffraction spot of interest and thedirectly transmitted spot in the experimental diffraction pattern, andΔL is the difference between L₁ and L₀.

FIG. 1 illustrates a related art system 100 for performing nano beamdiffraction (NBD) analysis.

As illustrated in FIG. 1, the system 100 includes a dual beam focusedion beam (DBFIB) device 110 for preparing a transmission electronmicroscopy (TEM) sample extracted from a structure (e.g., asemiconductor structure), and a TEM/NBD device 120 for performing NBDanalysis on the TEM sample to acquire diffraction data.

The DBFIB device 110 can obtain a parallel-sided sample from asemiconductor wafer. This specimen geometry removes thickness variationscontained within the sample.

The TEM/NBD device 120 may obtain strain data with about 5 nm spatialresolution and a 0.1% strain sensitivity.

SUMMARY

In view of the foregoing and other problems, disadvantages, anddrawbacks of the aforementioned conventional devices and methods, anexemplary aspect of the present invention is directed to a system andmethod of performing nano beam diffraction (NBD) analysis which mayprovide diffraction data having a sensitivity which is less than 0.1%.

An exemplary aspect of the present invention is directed to a system forperforming nano beam diffraction (NBD) analysis, including a focused ionbeam (FIB) device for preparing a transmission electron microscopy (TEM)sample, a broad beam ion mill for milling the TEM sample to remove asurface portion of the TEM sample, and a strain analyzer for performingNBD analysis on the milled TEM sample to acquire diffraction data.

Another exemplary aspect of the present invention is directed to amethod of performing nano beam diffraction (NBD) analysis, includingpreparing a transmission electron microscopy (TEM) sample, milling theTEM sample to remove a surface portion of the TEM sample, and performingNBD analysis on the milled TEM sample to acquire diffraction data.Another exemplary aspect of the present invention is directed to asystem for performing nano beam diffraction (NBD) analysis, including afocused ion beam (FIB) device for preparing a parallel-sidedtransmission electron microscopy (TEM) sample, a broad beam ion mill formilling the TEM sample to remove a surface portion from two parallelsides of the parallel-sided TEM sample which has been damaged by the FIBdevice and expose an underlying surface, the removed surface portion ofthe TEM sample can range in thickness from 1 nm to 45 nm, and a strainanalyzer for performing NBD analysis on the milled TEM sample to acquirediffraction data on the underlying surface, ideally the strain analyzerusing a TEM camera image resolution of at least 4000×4000 pixels toacquire the diffraction data (although it could be as few as 250×250pixels), such that the diffraction data comprises a sensitivity which isless than 0.1%.

Another exemplary aspect of the present invention is directed to amethod of performing nano beam diffraction (NBD) analysis, includingpreparing a parallel-sided FIB transmission electron microscopy (TEM)sample, further milling the TEM sample to remove a surface portion fromtwo parallel sides of the parallel-sided TEM sample which has beendamaged by the preparing of the FIB TEM sample and expose an underlyingsurface, the removed surface portion comprising a thickness in a rangefrom 1 nm to 45 nm, and performing NBD analysis on the milled TEM sampleto acquire diffraction data on the underlying surface, by using a TEMcamera image resolution of at least 4000×4000 pixels, such that thediffraction data comprises a sensitivity which is less than 0.1%.

Another exemplary aspect of the present invention is directed to amethod of performing strain analysis. The method includes performing afirst NBD analysis on a milled TEM sample from a strained region of astructure to acquire diffraction data, performing a second NBD analysison a milled reference TEM sample from an unstrained region of thestructure to acquire reference diffraction data, and comparing thediffraction data from the first NBD analysis with the referencediffraction data from the second NBD analysis to determine an amount ofstrain in the milled TEM sample. With its unique and novel features, thepresent invention provides a system and method of performing nano beamdiffraction (NBD) analysis which may provide diffraction data having asensitivity which is less than 0.1%.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of the embodiments ofthe invention with reference to the drawings, in which:

FIG. 1 illustrates a related art system 100 for performing nano beamdiffraction (NBD) analysis;

FIG. 2 illustrates a system 200 for performing nano beam diffraction(NBD) analysis, according to an exemplary aspect of the presentinvention;

FIG. 3 illustrates a TEM sample S (e.g., parallel sided sample) whichhas been separated from the structure 300 (e.g., semiconductor device)by the FIB device 210, according to an exemplary aspect of the presentinvention;

FIG. 4 illustrates the TEM sample S, according to an exemplary aspect ofthe present invention;

FIG. 5 illustrates a strain analyzer 520 (e.g., a TEM/NBD instrument),according to an exemplary aspect of the present invention;

FIG. 6 illustrates a method 600 of performing nano beam diffraction(NBD) analysis, according to an exemplary aspect of the presentinvention;

FIG. 7 illustrates a method 700 of performing strain analysis, accordingto an exemplary aspect of the present invention;

FIG. 8A illustrates a bright field TEM image of a semiconductor finFETgate (e.g., test structure), according to an exemplary aspect of thepresent invention;

FIG. 8B illustrates the same finFET gate as a DFSTEM image, according toan exemplary aspect of the present invention;

FIG. 8C illustrates a NBD pattern generated by the analysis on the samefinFET gate illustrated in FIGS. 8A and 8B using 4 k×4 k resolution,according to an exemplary aspect of the present invention; and

FIG. 9 provides a graph which plots the standard deviation of the NBDmeasurements in the tests performed by the inventors.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION

Referring now to the drawings, FIGS. 2-9 illustrate the exemplaryaspects of the present invention.

With the continual reduction in semiconductor device dimensionality, theshift to three dimensional device geometries (finFETs), and theintroduction of new materials (SiGe), strain engineering ofsemiconductor structures has become a valid method of architectingdevice electrical performance. Strain engineering in semiconductordevices is typically on the order of 1-2%. However, some researchdevices are looking to engineer strain in structures at less than 1%.

This has placed a demand on characterization techniques to providestrain information with a spatial resolution on the order of nanometersand a strain sensitivity of less than 0.1%. Thus, it is desired tomanufacture a transmission electron microscopy (TEM) sample withincreased nanobeam diffraction (NBD) sensitivity of less than 0.1%. Inparticular, it would be useful if improvements in sensitivity could beobtained while preserving the current TEM sample preparation process.

Precession electron diffraction (PED) TEM techniques may be able toachieve better sensitivity than conventional TEM NBD analyses, but thesetechniques require additional hardware and software on a TEM.

Further, related art systems and methods such as the related art systemin FIG. 1 (e.g., conventional FIB prepared samples), cannot providestrain sensitivity much less than 0.1%. This limit on sensitivity is dueto several factors including the damage to the TEM sample surfacescaused by the conventional FIB (e.g., DBFIB) TEM sample preparation.

The layer of damage to the surface of TEM samples which is caused by FIBis proportional in depth into the sample to the accelerating voltage ofthe incident gallium (Ga) ions. This relationship is about 1 nm per kV.

It is common practice to finish a TEM sample with 2-5 kV Ga ions andstrain samples are typically around 100 nm thick. As a result, about5-10% of the final sample thickness is structurally damaged—thecrystalline lattice of the materials in the sample has been amorphizedor otherwise distorted. These damage layers may introduce a subtleartifact into the NBD patterns which worsen the sensitivity of thetechnique.

The inventors have discovered that it may be possible to improve the NBDstrain sensitivity to be less than 0.1%, by removing the damage layerson the sample by preparing the TEM sample (e.g., by an in-situ method)in the FIB and subsequently removing a surface portion of the TEM sample(e.g., the Ga damaged material) with a broad beam (e.g., about 1 μm) ionbeam in another sample preparation tool.

Thus, an exemplary aspect of the present invention may apply a broadbeam ion mill after conventional FIB preparation to remove that damagedlayer on the surface of the specimen, to improve the NBD strainsensitivity. This exemplary aspect may overcome the deficiencies of therelated art systems and methods and achieve a strain sensitivity by NBDon the order of 0.08 to 0.07% which represents a 15-20% improvement overthe related art systems and methods.

FIG. 2 illustrates a system 200 for performing nano beam diffraction(NBD) analysis, according to an exemplary aspect of the presentinvention.

As illustrated in FIG. 2, the system 200 includes a focused ion beam(FIB) device 210 for preparing a transmission electron microscopy (TEM)sample, a broad beam ion mill 215 for milling the TEM sample to remove asurface portion of the TEM sample, and a strain analyzer 220 forperforming NBD analysis on the milled TEM sample to acquire diffractiondata. Unlike the related art system 100 in FIG. 1 which performs NBDanalysis on the TEM sample which has been damaged by the DBFIB 110, thesystem 200 mills the TEM sample to remove a surface portion (e.g.,damaged layer) of the TEM sample and performs NBD analysis on theadditionally milled TEM sample (e.g., on an underlying surface of theTEM sample which has been exposed by the milling).

Referring again to FIG. 2, the structure input to the FIB device (e.g.,the structure to be analyzed) may include semiconductor structure suchas a semiconductor wafer, a fin field effect transistor (finFET) and avertical field effect transistor (vFET). In particular, the structuremay include silicon, germanium, SiGe, etc.

The FIB device 210 may use a focused beam of ions (e.g., Ga ions) tomill (e.g., machine, cut, etc.) a TEM sample from the structure (e.g.,semiconductor device). The FIB device 210 may include, for example, adual beam FIB (DBFIB) which includes a scanning electron microscope(SEM) to view the TEM sample as the focused beam of ions mills the TEMsample from the structure.

For example, the FIB device 210 may include a gallium DBFIB tool used tomill and extract the TEM sample from the structure. The gallium DBFIBtool may generate an ion beam column based on setting an acceleratingvoltage in the range of about 0.5 kV to about 50 kV (typically 5 kV and30 kV), an ion beam current in the range of about 1 pA to about 10 nA(typically 50 pA-9 nA), and a tilt angle in the range of about 0 toabout 52 degrees (typically +/−2 degrees during TEM sample fabrication).The material sputter rate may vary according the ion beam current andaccelerating voltage, as well as tool design and set up.

The electron beam column of the DBFIB tool may include an acceleratingvoltage in the range of about 0.5 kV-50 kV (typically 5 kV). The beamdiameter of the ion beam may be about 1.0 nm to about 1000 nm, althoughsmall or larger beam diameters may be contemplated. Also, in operation,the ion beam may be rastered back and forth to cover an area which maybe, for example, over 100 μ×100 μm.

FIG. 3 illustrates a TEM sample S (e.g., parallel sided sample) whichhas been extracted from the structure 300 (e.g., semiconductor device)by the FIB device 210, according to an exemplary aspect of the presentinvention. The TEM sample S may be machined from the structure by theFIB device 210 by using an in situ lift-out technique, or by some othertechnique (e.g., H-bar technique, ex situ technique).

FIG. 4 illustrates the TEM sample S, according to an exemplary aspect ofthe present invention. As illustrated in FIG. 4, the TEM sample S may belifted out of the structure 300 by a probe and then transferred by theprobe and mounted onto a carrier 400 (e.g., a TEM half-grid) while it isstill in a chamber of the FIB device 210. Final FIB milling may beperformed while the TEM sample S is on the carrier 400.

After the final FIB milling, the TEM sample S may, for example, have awidth Ws in a range from 5 μm-10 μm, a depth Ds less than the width Wsand in a range from 2 μm-8 μm, and a thickness Ts smaller than the widthWs and the depth Ds and in a range from 50 nm to 150 nm.

The TEM sample S may then be transported out of a chamber of the FIBdevice 210 on the carrier 400 and placed in a chamber of the broad beamion mill 215. The broad beam ion mill 215 may be used to mill a surfaceof the TEM sample S in order to remove a surface portion of the TEMsample S which has been damaged by the milling performed by the FIBdevice 210. That is, the broad beam ion mill 215 may be used to exposeand underlying surface (e.g., a pristine surface) which has not beendamaged by the FIB device 210.

In particular, the TEM sample S may include a parallel-sided sample inwhich case the broad beam ion mill 215 may remove a surface portion fromtwo parallel sides of the plurality of sides S₁-S₄ of the parallel-sidedsample. For example, referring to FIG. 4, the broad beam ion mill 215may remove a surface portion (e.g., a damaged portion) from sides S₂ andS₄ which have an area of Ds×Ws. The surface portion to be removed mayinclude a thickness in a range from 5 nm to 15 nm.

As noted above, about 1 nm of the surface of the TEM sample S may bedamaged by the FIB device 210 per kV of accelerating voltage of theincident ion beam (e.g., gallium (Ga) ions). Thus, for example, wherethe TEM sample S is finished with 5 kV Ga ions in the FIB device 210,about 5 nm of a side (e.g., two parallel sides of the plurality of sidesS1-S4) will be removed by the broad beam ion mill 215.

In another exemplary aspect, to ensure that an undamaged surface (e.g.,a pristine surface) is exposed, the broad beam ion mill 215 may beconfigured to remove more than 1 nm (e.g., more than 1.5 nm) per kV Gaions. For example, in this exemplary aspect, where the TEM sample S isfinished with 5 kV Ga ions in the FIB device 210, about 7.5 nm of a side(e.g., two parallel sides of the plurality of sides S1-S4) will beremoved by the broad beam ion mill 215.

In another exemplary aspect, the broad beam ion mill 215 may beconfigured so that a side (e.g., two parallel sides of the plurality ofsides S1-S4) of the TEM sample S is inspected (e.g., by SEM) during themilling (e.g., continuously or periodically), and the milling is ceasedupon the inspection indicating that the surface is pristine (e.g.,sufficiently undamaged to provide an accurate strain measurement (e.g.,greater than 0.1% strain sensitivity)). For example, the TEM sample Smay be inspected after 1 nm per kV Ga ions, and if the inspectionreveals that the surface is not pristine, then the broad beam ion mill215 may mill another 0.1 nm per kV Ga ions a side, and so on, until thepristine underlying surface is exposed by the milling.

The broad beam ion mill 215 may utilize, for example, an argon ion beamhaving a size in a range from 0.5 μm to 1.5 μm. Further, the broad beamion mill 215 may be operated, for example, at a current in a range from0 μA to 300 μA and a voltage in a range from 0 eV to 2000 eV. In aparticular embodiment, the broad beam ion mill 215 may be operated at acurrent in a range from 120 μA to 150 μA and a voltage in a range from500 eV to 900 eV.

Referring again to FIG. 2, after the surface portion of a side of theTEM sample S (e.g., two parallel sides of the plurality of sides S1-S4of the TEM sample S) has been removed by the broad beam ion mill 215 toexpose an undamaged underlying surface, then the milling of the broadbeam ion mill 215 may be stopped, and the milled TEM sample Stransported on the carrier 400 out of the chamber of the broad beam ionmill 215 and into the strain analyzer 220. The strain analyzer 220 mayperform NBD analysis on the milled TEM sample S to acquire diffractiondata.

FIG. 5 illustrates a strain analyzer 520 (e.g., a TEM/NBD instrument),according to an exemplary aspect of the present invention. The strainanalyzer 220 may be similar in design to the strain analyzer 520. Thestrain analyzer 520 performs NBD analysis on the milled TEM sample S.

As illustrated in FIG. 5, the strain analyzer 520 includes a beamgenerator 521 (e.g., TEM unit) which generates a collimated electronbeam 522. The beam size of the electron beam in NBD mode 522 may be, forexample, in a range of 0.5 nm to 5 nm. The collimated electron beam 522is scattered off the atoms in the TEM sample S.

The strain analyzer 520 (e.g., TEM) also includes an objective lens 523through which the scattered beam is passed, onto a receiving unit 524(e.g., charge coupled device (CCD)) which generates a diffractionpattern (e.g., diffractogram) (e.g., see FIG. 8C).

The sensitivity of the NBD technique utilized by the strain analyzer 520may be determined by looking at the standard deviation of the NBDmeasurements in an unstrained region of the structure compared to thereference diffraction pattern taken from the same region of the sample.One standard deviation (a) of this data set is accepted as thesensitivity of the technique.

Referring again to FIG. 5, the strain analyzer 520 may also include aprocessing device 525 (e.g., computer, microprocessor, server, etc.)which is coupled to the receiving unit 524 and processes the diffractionpattern data generated by the receiving unit 524, and output the results(e.g., as a display on a display device). For example, the results maybe presented as a plot of strain as a function of position.

For example, the processing device 525 may execute a computer program(e.g., F-Strain or Epsilon) to read and fit NBD maps and profiles instandard format. The program may perform data analysis in three steps:First, each diffraction pattern is filtered using an auto-correlationalgorithm. Second, an algorithm locates a number (e.g., 30) of the mostinner reflections in the diffraction pattern. Third, a two dimensionalgrid is fitted to all (e.g., 30) spot locations, using the confidencelevel of each individual spot location (σ_(x), σ_(y)) as weight in thefit of the grid.

The base vectors of the grid are then compared to vectors imported fromunstrained material, and the strain is determined asε=(g_(ref)−g_(strain))/g_(strain). A special filtering feature may alsobe used in the analysis, which makes it possible to measure strain insemiconductor (e.g., silicon) devices even in the presence of othercrystalline materials covering the probed area, which is important forthe characterization of the next generation of devices (e.g., finFETs,VFETs, etc.).

NBD patterns are commonly taken at image resolutions ranging from 256pixels² up to 2048 pixels² (2 k). The higher the number of pixels in theimage, the smaller the detectable displacement of the diffraction spotswhich can be detected. The strain analyzer 520 of the present invention(e.g., microscope detector) may be capable of obtaining images with aresolution of 4096 pixels² (4 k). That is, the strain analyzer 520 mayuse a TEM camera image resolution of at least 4000×4000 pixels toacquire a diffraction pattern (e.g., diffraction data) for the milledTEM sample S.

Referring again to the drawings, FIG. 6 illustrates a method 600 ofperforming nano beam diffraction (NBD) analysis, according to anexemplary aspect of the present invention.

As illustrated in FIG. 6, the method 600 includes preparing (610) atransmission electron microscopy (TEM) sample, milling (615) the TEMsample to remove a surface portion of the TEM sample, and performing(620) NBD analysis on the milled TEM sample to acquire diffraction data.

FIG. 7 illustrates a method 700 of performing strain analysis, accordingto an exemplary aspect of the present invention.

In the method 700, a diffraction pattern (e.g., one or more diffractionpatterns) may be taken for a TEM sample Sin a strained region of thestructure 300, and a reference diffraction pattern (e.g., one or morereference diffraction patterns) may be taken in the unstrained region ofthe structure 300 (e.g., a single crystal region). The position of thediffraction points in the two diffraction patterns is compared. Theamount of displacement of the points may be considered to be due to thestress in the strained region and, therefore, a measure of strain in theTEM sample S.

As illustrated in FIG. 7, the method 700 includes performing (710) afirst NBD analysis on a milled TEM sample from a strained region of astructure to acquire diffraction data, performing (720) a second NBDanalysis on a milled reference TEM sample from an unstrained region ofthe structure (i.e., the same structure) to acquire referencediffraction data, and comparing (730) the diffraction data from thefirst NBD analysis with the reference diffraction data from the secondNBD analysis to determine an amount of strain in the milled TEM sample.

In the method 700, the milled TEM sample and the milled reference TEMsample may both be produced as discussed above for the TEM sample S(e.g., with the system 200). That is, for both the milled TEM sample andthe milled reference TEM sample, the FIB device 210 may be used toprepare a TEM sample and the broad beam ion mill 215 may be used to millthe TEM sample to remove a surface portion of the TEM sample and producethe milled TEM sample (e.g., the milled TEM sample and the referencemilled TEM sample).

EXAMPLES

The inventors have performed tests using the system 200 and methods 600,700, and the results of these tests are provided below.

For example, in one test, a sample was made on an advanced technologynode finFET test structure and analyzed in a 200 kV TEM equipped with a4 k camera and commercially available strain analysis software using asub 5 nm parallel probe. The data compared here was obtained on the samephysical gate and as a result it was possible to align subsequent NBDscans with respect to each other to ensure the same area of the samplewas being directly compared across data sets to within a few nanometersof positioning. The strain profile of the structure (not shown) exceeded1% strain which allowed straightforward alignment of the data.

FIG. 8A illustrates a bright field TEM image of the semiconductor finFETgate (e.g., test structure), according to an exemplary aspect of thepresent invention. FIG. 8B illustrates the same finFET gate as a DFSTEMimage. In addition, the line 850 in FIG. 8B indicates the line ofanalysis for acquiring NBD patterns on this sample. FIG. 8C illustratesa NBD pattern generated by the analysis on the semiconductor finFET gateillustrated in FIGS. 8A and 8B using 4 k×4 k pixel resolution, accordingto an exemplary aspect of the present invention.

In this test, the inventors determined that doubling the step size ofthe data acquisition from 5 nm per step (σ=0.0753) to 2.5 nm per step(σ=0.0716) changed in the sensitivity of the data by about 5%. It isimportant to note that the 2.5 nm data set contained twice the number ofdata points for calculating a compared to the 5 nm data set over thesame distance in the sample. Changing the image resolution from 2 k(σ=0.0867) to 4 k (σ=0.0753) showed an improvement in the standarddeviation of about 13% across 26 separate data points in eachacquisition.

After the above data was obtained, the sample was thinned using a broadbeam Argon (Ar) ion mill operating at 900 eV to remove the damage layeron either side of the sample. Unfortunately the sample was excessivelythinned (greater than 50% reduction in thickness) during this processand the original gate of analysis did not survive intact.

An alternative gate on the same sample was analyzed instead. When thesame data points in the sample were compared for σ, the pre Ar ion millsample had aσ of 0.0785 and the post Ar ion mill sample had a σ of0.0718. This is about an 8.5% improvement in σ.

As such a significant reduction in thickness of the sample could haveintroduced other effects (e.g. strain relaxation, significantly lessdiffraction events, etc.) upon a, a second sample was fabricated andanalyzed to determine if the removal of the damage layer has an impactupon G. The second sample was reduced in thickness on the order 15%.

The 2.5 nm step size and 4 k camera resolution were used to obtain thedata from the same gate in the sample for the comparison below. Thebefore and after Ar ion milling as were 0.099 and 0.083 respectivelyshowing an 18.5% improvement in σ.

FIG. 9 provides a graph which plots the standard deviation of the NBDmeasurements in the tests performed by the inventors. Each point in thegraph in FIG. 9 represents a standard deviation for 220 strain (e.g.,strain in the {220} direction) obtained from a diffraction pattern of aTEM sample extracted from a structure (e.g., semiconductor structure).As noted above, one standard deviation of the data set is accepted asthe sensitivity of the NBD technique.

All of the diffraction pattern images were obtained with a 4000×4000pixel camera setting. The ordinate of the graph is the standarddeviation of the diffraction pattern data obtained on the TEM sample,and the abscissa is the number of diffraction pattern images.

As illustrated in FIG. 9, the graph includes first standard deviationdata 980 for TEM samples which were not milled by the broad beam ionmill (i.e., TEM samples prepared by the related art system 100), andsecond standard deviation data 985 for TEM samples which were milled bythe broad beam ion mill (i.e., TEM samples prepared according to anexemplary aspect of the present invention). The graph also identifies afirst set 990 of the data 980, 985 which was taken from an unstrainedregion (e.g., including a sensitivity calculation region) of thestructure, and a second set 995 of the data 980,985 taken from astrained region of the structure.

As illustrated in FIG. 9, the standard deviation for the data 980obtained for samples prepared without the broad beam ion mill was0.0989, whereas the standard deviation for the data 985 obtained forsamples prepared with the broad beam ion mill was 0.0834, indicating asignificant improvement in sensitivity of strain data obtained by theNBD technique by use of the broad beam ion mill.

The various experimental parameters and their corresponding impact upona are summarized in Table 1 below.

TABLE 1 Experimental impact of parameters on σ Parameter % Improvementof σ Decreasing Step Size 5 Increasing Image 13 Resolution RemovingSample 18.5 Surface Damage

Thus, based on the tests conducted by the inventors, it was determinedthat oversampling the data acquisition by overlapping the NBD probe by50% (5 nm probe with 2.5 nm steps) leads to a negligible improvement inthe sensitivity of the technique. However, increasing the number ofpixels of each diffraction pattern from 2 k to 4 k (e.g., at least 4 k,or 4000×4000) and removing the FIB prepared sample surface damage bothshow improvements in NBD sensitivity greater than 10%. As a result, itis possible to obtain greater sensitivity of the NBD technique byemploying these changes in response to the evolving characterizationneeds.

With its unique and novel features, the present invention provides asystem and method of performing nano beam diffraction (NBD) analysiswhich may provide diffraction data having a sensitivity which is lessthan 0.1%.

While the invention has been described in terms of one or moreembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims. Specifically, one of ordinary skill in the art willunderstand that the drawings herein are meant to be illustrative, andthe design of the inventive method and system is not limited to thatdisclosed herein but may be modified within the spirit and scope of thepresent invention.

Further, Applicant's intent is to encompass the equivalents of all claimelements, and no amendment to any claim the present application shouldbe construed as a disclaimer of any interest in or right to anequivalent of any element or feature of the amended claim.

What is claimed is:
 1. A system for performing diffraction analysis,comprising: a mill for removing a surface portion of a sample; and ananalyzer for performing diffraction analysis on the milled sample. 2.The system of claim 1, further comprising: a focused ion beam (FIB)device for preparing the sample, the mill removing a surface portion ofthe prepared sample.
 3. The system of claim 2, wherein the diffractionanalysis comprises nano beam diffraction (NBD) analysis, the samplecomprises a transmission electron microscopy (TEM) sample, the millcomprises a broad beam ion mill for milling the prepared sample, and theanalyzer comprises a strain analyzer.
 4. The system of claim 3, whereinthe analyzer performs the NBD analysis on the milled sample to acquirediffraction data.
 5. The system of claim 4, wherein the milling of theTEM sample exposes an underlying surface of the TEM sample, and thestrain analyzer uses a TEM camera image resolution of at least 4000×4000pixels to acquire the diffraction data on the underlying surface.
 6. Thesystem of claim 4, wherein the surface portion removed by the broad beamion mill comprises a portion of the surface of the TEM sample which hasbeen damaged by the FIB device.
 7. The system of claim 4, wherein theTEM sample comprises a parallel-sided sample, and the broad beam ionmill removes a surface portion from two parallel sides of theparallel-sided sample.
 8. The system of claim 4, wherein the surfaceportion comprises a thickness in a range from 1 nm to 45 nm.
 9. Thesystem of claim 4, wherein the surface portion comprises at least 10% ofa thickness of the TEM sample, and wherein the diffraction datacomprises a sensitivity which is less than 0.1%.
 10. The system of claim4, wherein the structure comprises one of a fin field effect transistor(finFET) and a vertical field effect transistor (vFET).
 11. The systemof claim 4, wherein the broad beam ion mill is operated at a current ina range from 120 μA to 150 μA and a voltage in a range from 500 eV to900 eV, and utilizes an argon ion beam having a size in a range from 0.5μm to 1.5 μm.
 12. A method of performing diffraction analysis,comprising: removing a surface portion of a sample; and performingdiffraction analysis on the removed surface portion of the preparedsample.
 13. The method of claim 12, further comprising: before removingthe surface portion of the sample, preparing the sample.
 14. The methodof claim 13, wherein the diffraction analysis comprises nano beamdiffraction analysis, the sample comprises a transmission electronmicroscopy (TEM) sample, the removing of the surface portion comprisesmilling the prepared sample, and the performing of the NBD analysiscomprises using a strain analyzer to perform the NBD analysis.
 15. Themethod of claim 14, wherein the NBD analysis is performed on the milledsample to acquire diffraction data.
 16. The method of claim 15, whereinthe milling of the TEM sample exposes an underlying surface of the TEMsample, and the strain analyzer uses a TEM camera image resolution of atleast 4000×4000 pixels to acquire the diffraction data on the underlyingsurface.
 17. The method of claim 15, wherein the preparing of the TEMsample is performed by using a focused ion beam (FIB) device, themilling of the TEM sample is performed by using a broad beam ion mill,and the surface portion comprises a portion of the surface of the TEMsample which has been damaged by the FIB device.
 18. The method of claim17, wherein the milling of the TEM sample is performed by a broad beamion mill which is operated at a current in a range from 120 μA to 150μand a voltage in a range from 500 eV to 900 eV and utilizes an argon ionbeam having a size in a range from 0.5 μm to 1.5 μm, and wherein the TEMsample comprises a parallel-sided sample, and the broad beam ion millremoves a surface portion from two parallel sides of the parallel-sidedsample.
 19. A method of performing strain analysis, comprising:acquiring diffraction data for a sample; acquiring reference diffractiondata for a reference sample; and comparing the diffraction data with thereference diffraction data to determine an amount of strain in thesample.
 20. The method of claim 19, wherein the sample is from astrained region of a structure and the acquiring of the diffraction datacomprises performing a first strain analysis on the sample, and whereinthe reference sample is from an unstrained region of the structure andthe acquiring of the reference diffraction data comprises performing asecond strain analysis on the reference sample.